I have had Vonage for a bit over two years and am fairly satisfied with it (I have cable internet). I also got a line for my daughter and son-in-law in South Dakota (I'm in Arizona), so that works very well when Mom and daughter (an me and SIL) have SIX HOUR conversations (Thank GAWD for hands-free phone sets!!).
Vonage support is pretty dismal (in the Philippines), but the set up is easy and I've never has any significant issues.
On the other hand their competitor, VOIP.com is an outright bunch of frauds and virtually make no bones about it.
My wife used Vonage to talk to her aunt in Soctland a few times before she passed on, but I think Vonage now has an extra fee for international calls (I think it's $5 a month).
One note, though: if you use a FAX, it won't work over a Vonage line, but they do have a FAX line option for $10/month)